The present invention relates to a composition for coating which contains a radiation-curable compound, more particularly, a radiation-curable composition for coating which can form an ink receiving layer, on which image information and literature information can be printed with an ink jet method.
The present invention also relates to an optical recording medium having an ink receiving layer formed of the radiation-curable composition for coating.
Recently, in an optical recording medium, there has been a greater demand for providing a surface opposite to a surface on which optical writing/reading is performed, with an ink receiving layer (lebel printing surface) and printing images or literatures representing a recorded content in the medium with an ink jet method so as to arrange the optical recording medium.
As an ink used for an ink jet recording method, there is usually used an aqueous one and, in many cases, a polyhydric alcohol or the like is added to this ink in order to prevent clogging of a nozzle.
On the other hand, as a substrate on which recording is made in the ink jet recording method, there have hitherto been used a normal paper, and a hydrophilizied paper such as a specialty paper for ink jet which is provided with a porous ink receiving layer. As such an ink receiving layer, there are described, for example, the use of a water-soluble high polymer of poly (vinyl alcohol) and polyacrylic acid in Japanese Laid-open Patent Publication No.60-168651/1985, the use of hydroxyethyl cellulose in Japanese Laid-open Patent Publication No.60-262685/1985, the use of a mixture of carboxymethyl cellulose and polyethylene oxide in Japanese Laid-open Patent Publication No.61-181679/1986, and the use of a mixture of water-soluble cellulose and poly (vinylpyrrolidone) in Japanese Laid-open Patent Publication No.61-193879/1986. Since the water-soluble polymers described in these laid open publications are very hydrophilic, they have affinity with a hydrophilic substrate such as a paper and the like and, when an ink receiving layer composed of these water-soluble polymers is provided on the surface of a hydrophilic substrate, there arises no problem on adhesion between the substrate and the ink receiving layer .
However, for example, the water-soluble polymers described in the aforementioned laid open publications have little affinity with substrates having the surface of strong hydrophobicity such as an ultraviolet-curing resin and the like frequently used in a protecting membrane for the optical recording medium. For that reason, when an ink receiving layer composed of these water-soluble polymers is provided on the surface of a hydrophobic substrate, adhesion between the hydrophobic substrate and the ink receiving layer is worse and, after laminated, they are easily peeled and, additionally, since the ink receiving layer itself has the lower water-resistance, there are occurrence of an ink blot caused by a water droplet after printing and stickiness of the surface, which leads to a problem of practical use.
Therefore, an object of the present invention is to provide a composition for coating which overcomes the aforementioned problems of the prior art, and which can form, in one coating step, an ink receiving layer which is excellent in clearness of an image and quick-drying and which is excellent in adhesion with a hydrophobic substrate, the water-resistance and the stability of printing such as no occurrence of printing fall or no occurrence of separation of the whole layer even when wiped after wetting with water.
An another object of the present invention is to provide an optical recording medium having an ink receiving layer formed of this composition for coating.
The present inventor studied intensively and, as a result, found that the aforementioned objects can be attained by a composition comprising a radiation-curable acrylic compound with a water-absorbing organic filler and a water-absorbing inorganic filler added, which resulted in the completion of the present invention.
That is, the present invention is a composition for coating which comprises a radiation-curable compound (A) containing a monofunctional (meth) acrylic monomer and multifunctional more than bifunctional (meth) acrylic monomer, a water-absorbing organic filler (C) and a water-absorbing inorganic filler (D).
In the composition of the present invention, the radiation-curable compound (A) preferably contains 50-90% by weight of the monofunctional (meth) acrylic monomer and 10-50% by weight of the multifunctional more than bifunctional (meth) acrylic monomer.
In the composition of the present invention, the composition preferably contains 10-60% by weight of the water-absorbing organic filler (C) and 1-20% by weight of the water-absorbing inorganic filler (D) relative to the radiation-curable compound (A).
In the present composition, a particle size of the filler (C) and (D) is preferably 0.001 to 20 xcexcm.
In the composition of the present invention, the composition preferably contains 0.001 to 10% by weight of a polymerization initiator relative to the radiation-curable compound (A).
The present invention is also a recording material having an ink receiving layer composed of a radiation-cured aforementioned composition for coating on at least one side of a hydrophobic supporting substrate.
The present invention is also an optical recording medium having an ink receiving layer composed of a radiation-cured aforementioned composition for coating on the surface opposite to the surface of the optical recording medium on which optical writing/reading is performed.